Polymethacrylate viscosity index improvers (PMA VII's) are well known in the lubricating industry. Many attempts have been made to produce PMA VII's that have the desired balance of high temperature and low temperature viscometrics, as well as the required shear stability for a given application. The present invention is directed to novel non-dispersant (meth) acrylate copolymers which exhibit the necessary high and low temperature viscometrics as well as the necessary shear stability for numerous lubricating applications.
U.S. Pat. No. 4,021,357 is directed to multifunctional tetrapolymer lube oil additives. These tetrapolymers are dispersant polymethacrylates containing specific ratios of C1-C5, C10-C15 and C16-C20 (meth) acrylate monomers as well as a dispersant monomer. The copolymers of the present invention do not contain a dispersant monomer. Further, the copolymers of the present invention contain butyl methacrylate, a C10-C15 (meth) acrylate and a C16-C30 (meth) acrylate in proportions outside the ranges taught in the '357 patent.
U.S. Pat. No. 4,606,834 is directed to dispersant viscosity index improvers for lube oils containing a terpolymer of lauryl methacrylate, stearyl methacrylate and N,N-dimethylaminopropyl methacrylamide. The polymers of the present invention contain butyl methacrylate and do not contain a methacrylamide dispersant monomer.
U.S. Pat. No. 4,867,894 discloses pour point improving additives for mineral oils comprising from 10 to 30 mole percent methyl methacrylate, 10 to 70 mole percent of a linear C16 to C30 alkyl methacrylate, from 10 to 80 mole percent of a C4-C15 linear alkyl methacrylate and/or a C4 to C40 branched methacrylate, and from 0 to 30 mole percent of a free-radically polymerizable nitrogen-containing monomer having dispersing action. The polymers of the present invention do not contain methyl methacrylate or a dispersant monomer and contain less than 10 mole percent of the linear C16-C30 alkyl methacrylate.
U.S. Pat. No. 5,112,509 teaches a method for making a methyl methacrylate-lauryl methacrylate copolymer. This patent does not teach the copolymers of the present invention, which require butyl methacrylate and a C16-C30 (meth) acrylate.
U.S. Pat. Nos. 5,312,884 and 5,368,761 disclose copolymers useful as pour point depressants for lubricating oils comprising 15-67 mole percent C8-C 15 alkyl (meth) acrylates, 3-40 mole percent C16-C24 (meth) acrylates, and from greater than 30-65 mole percent C1-C4 methacrylates. These patents do not teach copolymers containing the specific monomers in the specific proportions required by the present claims. Further, these references do not teach that the copolymers are useful viscosity index improvers for lubricating oils.
U.S. Pat. No. 5,534,175 discloses copolymers of unsaturated fatty esters derived from 12-20 mass % of a C1-C3 (meth) acrylate, 45-72 mass % of a C11-C15 (meth) acrylate and 14-30 mass % of a C16-C25 (meth) acrylate. This patent does not teach the copolymers of the present invention which contain butyl methacrylate. Further, this patent fails to teach the specific monomer proportions required for the present invention.
EP 0 236 844 B1 teaches pour point improving agents derived from methyl methacrylate. This patent fails to teach the specific copolymers of the present invention or their use as viscosity index improvers for lubricating oils.
EP 0 439 254 A2 is directed to dispersant polymethacrylate viscosity index improvers. This application does not teach the specific non-dispersant viscosity index improvers of the present invention.